A disease associated with squalor could be on the increase in suburban homes because more people are keeping rodents as pets, warns an Australian microbiologist.

Known as rat bite fever, the disease can result after a bite, scratch or exposure to excreta or saliva from rodents such as rats, guinea pigs, gerbils and ferrets.

Dr Shivanti Abeysuriya of PathWest Laboratory Medicine at the Queen Elizabeth II Medical Centre in Perth says rat bite fever was previously associated with those living in poverty in rat-infested buildings.

"Now that rats are becoming popular pets and study animals, cases are increasingly seen in different groups of people such as pet owners, pet shop workers and laboratory technicians," she says.

"The message to the public is that keeping rats as pets and handling them can be hazardous to their health."

According to Abeysuriya the risk of infection after a bite is about 10% and if untreated could result in death for 1 in 10. Complications include endocarditis (infection in the heart valves), meningitis, septic arthritis and focal abscesses.

Abeysuriya says people should be aware of the risk of infection and handle their rodent pets carefully.

"Scientists who handle rats know about the infection and take preventive measures such as wearing gloves," she says.

After a rodent bite the wound should be thoroughly cleaned with soap and water and owners should report symptoms to their doctor immediately.

Abeysuriya says doctors should be aware that rat bite fever is an emerging disease.

"More people are keeping rodents as pets and should suspect this infection in patients with a suggestive clinical picture," she says.

Case study

Abeysuriya outlines the case of a Western Australian girl who was diagnosed with the fever.

The girl, 13, arrived at hospital with a rash covering her body plus fever, headache, vomiting and suffered from joint pain for two days.

She denied she had been bitten or scratched by her pet rat, but said she played with it and cleaned its cage.

Tests detected a bacterial infection (Streptobacillus moniliformis) in the girl's blood, a bacteria found in rats' upper respiratory tracts.

"Most rats are asymptomatically colonised (showing no signs of illness) with this bacteria in their mouth and upper respiratory tract," says Abeysuriya.

"Not all rats would have this infection and only a percentage would be colonised, but you don't know which rat is colonised and which is not."

Other sources

Abeysuriya warns that other domestic pets could be responsible for transmitting infection.

"Sometimes cats and dogs that feed on or attack rodents can get transiently colonised and there is a human case report of rat bite fever resulting from a bite from a greyhound which ate rodents," she says.

Abeysuriya says rat bite fever can be difficult to diagnose because signs and symptoms are non-specific, and may appear to be the result of other bacterial and viral infections.

The diagnosis can also take several days as the organism grows slowly in the laboratory.

Since first reported in the US in 1839, there have been more than 200 cases of the rare zoonotic infection documented worldwide, mostly in North America. Australia has recorded less than 10 cases since 1940, but Abeysuriya believes that figure could be higher as many may have gone unreported.